This invention relates to precision cutting of discrete devices such as semiconductor devices, more particularly, to a diamond dicing blade used for efficient and symmetric cutting with reduced chipping.
There are many prior art discrete devices which are formed as a plurality of substrates integrally formed in a wafer or the like which require intermediate cuts and/or separation into individual subunits as a last step in the fabrication process. Examples of such discrete devices are semiconductor devices. Most, but not all, of the devices are formed in silicon-based wafers. A preferred technique for separating the sub-units is to saw through the wafer in a procedure referred to as xe2x80x9cdicing.xe2x80x9d The device used to perform the cutting is referred to as a dicing blade. For cutting operations requiring high precision (+/xe2x88x920.5 micron), diamond blades have been preferred, especially in the production of semiconductor devices, because they form precisely placed cuts.
However, these prior art diamond blades still suffer from performance variability manifested in the asymmetric chipping of the wafer due to the forces generated when pieces of silicon particles loosen from the wafer between the rotating dicing blade and the silicon wafers being cut.
For instance, as shown in FIG. 1a, silicon wafer 8 having a frontside 10 and backside 12 is diced by a dicing blade 6 with large diamond particles 14, with a mean particle size of about 5-6 microns. Large diamond particles 14 allow for an increased feed rate or throughput and produce good backside chipping 18. However, when large particles 14 are used they present the problem of poor frontside chipping 16 due to the increased contact area/pressure between the large particle 14 and frontside 10. Hence, symmetric dicing on the frontside 10 and backside 12 is problematic. The large degree of frontside chipping is especially a problem because of its proximity to the fabricated circuitry which is located on wafer frontside 10.
In contrast, as shown in FIG. 1b, silicon wafer 8 having a frontside 10 and backside 12 may be diced by a dicing blade 4 with small diamond particles 20, with a mean particle size of about 1-2 microns. The small particle 20 provides minimal contact area with frontside 10 thereby allowing minimal pressure and producing good frontside chipping 3. But, small diamond particles 20 do not cut as efficiently as large particles 14 and using small particles 14 creates pressure buildup at the leading edge of the dicing blade 4 thereby causing chips to breakout (xe2x80x9csliveringxe2x80x9d), creating poor backside chipping 2.
Therefore what is needed is a diamond dicing blade which produces efficient, symmetric cuts with reduced chipping on both the frontside and backside of a wafer.
The present invention provides a multi-layered diamond dicing blade. More particularly, the blade is a multi-layered dicing blade comprising an inner layer with a first set of diamond particles and an outer layer overlying the inner layer. The inner layer extends to the outermost periphery of the dicing blade. The outer layer comprises a second set of diamond particles having a size smaller than the first set of diamond particles. The first set of diamond particles makes initial contact with the silicon wafer penetrating the bare silicon. The second set of diamond particles of the dicing blade provides a fine finish.
The above advantages and features of the invention will be more clearly understood from the following detailed description which is provided in connection with the accompanying drawings.